Robust Partitioned Scheduling for Static-Priority Real-Time Multiprocessor Systems with Shared Resources

International audienceWe focus on the partitioned scheduling of sporadic real-time tasks with constrained deadlines. The scheduling policy on each processor is static-priority. The considered tasks are not independent and the consistency of these shared data is ensured by a multiprocessor synchronization protocol. Considering these assumptions, we propose a partitioned scheduling algorithm which tends to maximize the robustness of the tasks to the Worst Case Execution Time (WCET) overruns faults. We describe the context of the problem and we outline our solution based on simulated annealing

Sustainability in static-priority restricted-migration scheduling

International audienceIn this paper, we focus on the static-priority scheduling of periodic hard real-time tasks upon identical multiprocessor platforms. In order to bound the inter-processor migrations, we consider the restricted-migration scheduling policy for which a task is allowed to migrate only at job boundaries. Several jobs of the same task can then be assigned on different processors but a given job can not migrate. It has been shown that this scheduling policy can suffer from scheduling anomalies. These anomalies occur when a decrease in execution requirement of a job causes a deadline miss. We present a static-priority restricted-migration scheduling algorithm and we prove it does not suffer from these anomalies. We also review the scheduling anomalies according to the scheduling tests for this algorithm

Worst case analysis of TreeMap data structure

International audienceData structures with relaxed balance eases the update of shared resources on asynchronous parallel architectures. This improvement is obtained by a better locking scheme of the data structure. In this paper, we describe the complexity and analyze the worst case cost of access operations on such a structure. We propose a data structure with the same properties as Java TreeMap but implemented with chromatic search tree; a tree with relaxed balance. The aim of our structure is to provide a more efficient TreeMap we can use in concurrent and real-time applications

Improvement of schedulability bound by task splitting in partitioning scheduling

International audienceWe focus on the class of static-priority partitioning scheduling algorithm on multiprocessor. We are interested in improving the schedulability of these algorithms by splitting the tasks which cannot be successfully allocated on processors

Partitioned Scheduling of Parallel Real-time Tasks on Multiprocessor Systems

International audienceIn this paper, we focus on the scheduling of periodic fork-join real-time tasks on multiprocessor systems. Parallel real-time tasks of fork-join model have strict parallel segments with no laxity. We propose a partitioned scheduling algorithm which increases the laxity of the parallel segments and therefore the schedulability of tasksets of this model. A similar algorithm has been proposed in the literature but it produces job migrations. Ours avoid the use of job migrations in order to create a portable algorithm that can be implemented on a standard Linux kernel. Results of extensive simulations are provided in order to analyze the schedulability of the proposed algorithm compared to the previous one

Performance Analysis for Segment Stretch Transformation of Parallel Real-time Tasks

International audienceThe Segment Stretch Transformation (SST) is an algorithm that transforms parallel Fork-Join (FJ) tasks into sequential tasks on multiprocessor systems when possible, in order to increase the schedulability of the tasksets of this model. SST is based on Task Stretch Transformation (TST) which is a transformation for the same model of tasks, but it uses segment migrations while SST eliminates their use. In this paper, we prove that SST transformation has the same performance of TST transformation by providing a detailed analysis based on Demand Bound Function (DBF) and by showing that SST has a resource augmentation bound of 3.42, same as TST, which means that if a taskset is feasible on m speed processors, then it is schedulable using the transformation on m processors that are 3.42 times faster

YARTISS: A Generic, Modular and Energy-Aware Scheduling Simulator for Real-Time Multiprocessor Systems

In this report, we present a free software written in Java, YARTISS, which is a real-time multiprocessor scheduling simulator. It is aimed at comparing user-customized algorithms with ones from the literature on real-time scheduling. This simulator is designed as an easy-to-use modular tool in which new modules can be added without the need to decompress, edit nor recompile existing parts. It can sim-ulate the execution of a large number of concurrent periodic independent tasksets on multiprocessor platforms and generate clear visual results of the scheduling process (both schedules and tunable metrics presentations). Other task models are already implemented in the simulator, like graph tasks with precedence constraints and it is easily extensible to other task models. Moreover, YARTISS can simulate tasksets in which energy consumption is a scheduling parameter in the same manner as Worst Case Execution Time (WCET)

Global EDF scheduling of directed acyclic graphs on multiprocessor systems

International audienceIn this paper, we study the problem of real-time scheduling of parallel tasks represented by a Directed Acyclic Graph (DAG) on multiprocessor architectures. We focus on Global Earliest Deadline First scheduling of sporadic DAG tasksets with constrained-deadlines on a system of homogeneous processors. Our contributions consist in analyzing DAG tasks by considering their internal structures and providing a tighter bound on the workload and interference analysis. This approach consists in assigning a local offset and deadline for each subtask in the DAG. We derive an improved sufficient schedulability test w.r.t. an existing test proposed in the state of the art. Then we discuss the sustainability of this test

YARTISS: A Tool to Visualize, Test, Compare and Evaluate Real-Time Scheduling Algorithms

International audienceIn this paper, we present a free software written in Java, YARTISS, which is a real-time multiprocessor scheduling simulator. It is aimed at comparing user-customized algorithms with ones from the literature on real-time scheduling. This simulator is designed as an easy-to-use modular tool in which new modules can be added without the need to decompress, edit nor recompile existing parts. It can simulate the execution of a large number of concurrent periodic independent task sets on multiprocessor systems and generate clear visual results of the scheduling process (both schedules and tunable metrics presentations). Other task models are already implemented in the simulator, like graph tasks with precedence constraints and it is easily extensible to other task models. Moreover, YARTISS can simulate task sets in which energy consumption is a scheduling parameter in the same manner as Worst Case Execution Time (WCET)

Temporal safety for real-time multiprocessor systems

Les systèmes temps réel à contraintes temporelles strictes sont caractérisés par des ensembles de tâches pour lesquelles sont connus l'échéance, le modèle d'arrivée (fréquence) et la durée d'exécution pire cas (WCET). Nous nous intéressons à l'ordonnancement de ces systèmes sur plate-forme multiprocesseur. Garantir le respect des échéances pour un algorithme d'ordonnancement est l'une des problématiques majeures de cette thématique. Nous allons plus loin en nous intéressant à la sûreté temporelle, que nous caractérisons par les propriétés (i) de robustesse et (ii) de viabilité. La robustesse consiste à proposer un intervalle sur les augmentations(i-a) de WCET et (i-b) de fréquence tel que les échéances soient respectées. La viabilité consiste cette fois à garantir le respect des échéances lors du relâchement des contraintes (ii-a) de WCET (réduction), (ii-b) de fréquence (réduction) et (ii-c) d'échéance(augmentation). La robustesse revient alors à tolérer l'imprévu, tandis que la viabilité est la garantie que l'algorithme d'ordonnancement n'est pas sujet à des anomalies suite à un relâchement de contraintes. Nous considérons l'ordonnancement en priorités fixes, où chaque occurrence d'une tâche est ordonnancée avec la même priorité. Dans un premier temps, nous étudions la propriété de robustesse dans les approches d'ordonnancement hors-ligne et sans migration (partitionnement). Nous traitons le cas des tâches avec ou sans partage de ressources. Dans un second temps, nous étudions la propriété de viabilité d'une approche d'ordonnancement en ligne avec migrations restreintes et sans partage de ressourcesThe hard real-time systems are characterized by sets of tasks for which are known the deadline, the arrival model (frequency) and the Worst-Case Execution Time (WCET). We focus on the scheduling of these systems on multiprocessor platforms. One of the main issues of this topic is to ensure that all deadlines are met. We go further by focusing on the temporal safety which we characterized by the properties of (i) robustness and (ii) sustainability. The robustness consists in providing an interval on the increases of (i-a) WCET and (i-b) frequency in such a way that the deadlines are met. The sustainability consists in ensuring that no deadline is missed when the following constraints are relaxed : (ii-a) WCET (decreasing), (ii-b) frequency (decreasing) and (ii-c) deadline (increasing). The robustness amounts to tolerate unexpected behaviors while the sustainability is the guarantee that the scheduling algorithm does not suffer from anomalies because of a relaxation of constraints. We consider fixed-priority scheduling for which any job of a task is scheduled with the same priority. Firstly, we study the property of robustness in off-line scheduling approaches without migration (partitioning). We deal with the case of tasks with or without shared resources. Secondly, we study the property of sustainability of an online restricted-migration scheduling approach without shared resource